Measurement of leucine metabolism in man from a primed, continuous infusion of L-1-3Cleucine

Leucine metabolism in vivo can be determined from a primed, continuous infusion of L-1-13Cleucine by measuring, at isotopic steady state, plasm -13Cleucine enrichment, expired 13CO2 enrichment, and CO2 production rate. With an appropriate priming dose of L-1-13Cleucine and NaH13CO3, isotopic steady state is reached in less than 2 h, and the infusion is completed in 4 h. The method can determine rates of leucine turnover, oxidation, and incorporation into protein with typical relative uncertainties of 2, 10, and 4%, respectively. The method requires no more than 1 ml of blood and uses stable isotope rather than radioisotope techniques. Thus, the method is applicable to studies of human beings of all ages. L-1-13Cleucine may be infused with a second amino acid labeled with 15N for simultaneous determination of the kinetics of two amino acids.